Electroplating process



ELEcTRoPtA'riNG PROCESS No Drawing. Application July 8, 1954 Serial N 0. 442,199

Claims priority, application Germany September 19, 1953 14 Claims. 01. 204-44 This invention relates to an improvement in electroplating and more particularly to electroplating baths modified with an organic sulfonic acid addition agent which will produce a bright and lustrous electro deposit.

Electroplating baths have heretofore been modified by the inclusion of organic sulfonic acids or organic sulfation products of various compounds. While the prior art addition agents have usually effected some improvement in the characteristics of the electro deposit produced from such modified baths, the additives individually have not been sufficient to produce commercially desirable deposits and had to be used with another and sometimes with even two or more supplemental addition agents.

It is an object of the invention to provide electroplating compositions of improved character.

Another object of the invention is to provide an electroplating bath which will produce bright and lustrous electro deposits which in many instances may be used for their intended purpose without further polishing or buffing.

Still another object of the invention is to provide addition agents for electroplating baths which may advantageously be used as sole addition agents or with other addition agents to produce bright and lustrous deposits.

Still further objects and advantages will become apparent as the description of the invention proceeds.

We have found that bright, highly lustrous and welladhering electroplate deposits can be obtained by modifying electroplating baths containing the metal to be deposited primarily in the form of an acid solution of an inorganic salt of the metal with organic sulfonic acids or their salts having the general structural formula wherein G represents an organic radical which comprises a carbon atom bonded exclusively to hetero atoms and to the radical R SO H through a sulfur atom and R represents a bivalent aliphatic radical which may be unsubstituted or may carry other organic substituents, such as, for example, ethylene, propylene, alkyl propylene, hydroxy propylene, pentylene radicals.

In other words the brightening agents used in accordance with the present invention are organic sulfonic acids or salts thereof which have the general structural States Patent Patented Aug. 26, 1958 lCe CS--RSOsH Y and their salts, wherein X and Y are selected from the group consisting of nitrogen, sulfur and oxygen atoms.

Typical sulfonic acids or their salts which can a dvantageously be used, either individually or in combination with each other, as brightening agents in electroplating baths in accordance with the present invention are the following:

1(1) Sulfonic acids derived from thiourea and, if the cation chain is closed, from Z-thioimidazoles or Z-benzene imidazoles, having the following structural formula:

C-SR.SO3H

(2) Sulfonic acids derived from Z-mercaptothiazoles or 2-mercapt0benzene thiazoles and from thiocyanates, having the following structural formula:

t3s-R.sOiH

(3) Sulfonic acids derived from 2-thiobenzoxazoles and 2-thiocumazoles (2-thiobenzene-metoxazine), having the following structural formula:

(4) Sulfonic acids derived from dithiocarbamic acids, having the following structural formula:

(5) Sulfonic acids derived from thioxanthic acid or trithiocarbonic acid, having the following structural formula:

O-SR.SOsH

(6) Sulfonic acids derived from xanthic acid, having the following structural formula:

0 s-R.s0tH

(7) Sulfonic acids derived from carbaminothiol acids, having the following structural formula:

CSR.SO3H

In all of the above representative examples of sulfonic 1 acids suitable for use as brightening additives for the specific salts of sulfonic acids of the above general classes acid-n-propylestenet-sodium N-butyl-dithiocarbamic acid-n-butylester-w-sodium sulfonate;

N-p-tolyl-dithiocarbamic acid-n-propylester-w-potassium sulfonate;

Dithiocarbamic acid-n-propylester-ammonium sulfonate; S-phenyl-trithiocarbonic acid-n-propylester-w-sodium sulfonate;

Trithiocarbonic acid-bis-propylester-w-sodium sulfonate; Isopropyl-xanthic acid-n-butylester-w-sulfonate of sodium; n-butyl-xanthic acid-n-propylester-w-sodium sulfonate; Carbamino-thiol acid-n-propylester-potassium sulfonate; and the like.

The specific sulfonic acid salts listed above for the purpose of illustrating the invention, but not of limiting the invention thereof, can be used as brightening agents in all types of electroplating baths, and particularly in electroplating baths for electrodepositing nickel, copper, zinc, silver, bronze and brass. They are capable of producing bright and lustrous deposits either individually or in conjunction with other well-known brightening agents, salts which improve the conductivity of the electroplating bath, wetting agents, or agents which tend to reduce the porosity of the deposit. above brightening agents are suitable for use in conjunction with those additives disclosed in German Patents No. 863,159 and No. 871,392.

It is well known in the art that the amount of brightening agent added to an electroplating bath in order to produce a bright and lustrous deposit lies between certain limits within which the desired results will be obtained. These limits are different for each individual agent. It is also known that the range of current densities which will produce a bright and lustrous deposit lies between certain limits and those limits depend large- 1y upon the type and amount of agent used and the temperature of the electroplating bath. We have found that the addition of organic sulfonic acids in accordance with the invention as brightening agents for electroplating baths will increase the range of current densities over which deposits of satisfactory character can be produced. The amounts in which compounds of the invention are added to electroplating baths to produce bright and lustrous deposits vary between 0.01 and gm. per liter of bath. The current density limit within which the above amounts will produce bright and lustrous deposits lies between 0.5 and 12 amp./drn. at a temperature below 60 C. By employing a mixture of the brighten ing agents disclosed herein, it is possible to further widen the range of current densities which will produce satisfactory bright and lustrous deposits.

Non-precious metals to be electroplated, such as, for example, iron, steel or zinc, to mention only a few, are usually first provided with a base coating of copper in a potassium cyanide bath before being finally electroplated with the desired metal. The brightening agents of this invention are suitable for use in electroplating objects pro-coated in this manner as well as in electroplating objects not so pre-coated.

In particular, the

Metal electro deposits produced from baths modified with the sulfonic acid additives of this invention are bright, highly lustrous and adhere very firmly to the base. In most cases the luster of the electro deposit so produced is so high that the electroplated object requires no further polishing or buffing after rinsing, whereby this additional time-consuming and costly step can be omitted in the production of electroplated articles. Moreover, the sulfonic acid brightening agents of this invention have the additional advantage that they are chemically resistant to acid conditions, so that electroplating baths modified with such additives can remain in use virtually continuously, even at high temperatures, without losing their intended effectiveness.

The following examples will enable persons skilled in the art to understand our invention more completely. It. is understood, however, that these examples are merely representative of the general inventive concept and that we do not intend to limit our invention to their exact conditions.

Example I 0.5 to 1 gm. of N,N-diethyl-dithiocarbarnic acid-npropylester-w-sodium sulfonate was added to each liter of an acid copper sulfate bath which contains 60 gm. sulfuric acid and gm. crystallized copper sulfate per liter of solution. Sheet steel provided with a preliminary copper coating in the presence of potassium cyanide was electroplated in the above bath. Within a current density range of from 1 to 10 amp./dm. at room temperature, both flat and highly profiled sheet steel objects were provided with a highly lustrous and well-adhering copper plate which did not require any further polishing or buffing treatment after rinsing.

Example II 0.5 to 1.5 gm. 2-rnercaptobenzenethiazole-S-propanew-sodium sulfonate are added to each liter of the electroplating bath of Example I. An object electroplated in this solution at room temperature within current density limits of 7.5 to 10 amp./dm. was provided with a copper coating which was highly lustrous and did not need any further polishing treatment.

Example III 1 gm. of betaine salt of isothiourea-S-propane-w-sulfonic acid was added to each liter of the electroplating bath of Examples I and II. An object electroplated in this solution at room temperature and current densities between 6 and 7.5 amp./dm. was provided with a highly lustrous copper coating which required no further polishing treatment after rinsing.

Example I V Example V The same effect as in Example IV was obtained by adding 1 gm. of n-butylxanthic acid-n-propylester-w-sodium sulfonate per liter of acid copper sulfate solution of Example IV to such a solution and electroplating at the same temperature, but with a current density of 4 to 6 amp./dm.

Example V1 0.5 to 1 gm. of the betaine salt of isothiourea-S-butanew-SlllfOHlC acid was dissolved in each liter of a nickelplating bath containing 60 gm. nickel chloride, 220 gm. crystallized nickel sulfate and 35 gm. boric acid per liter of solution. An object electroplated in such a solution at room temperature and current densities between 1 and amp./dm. was provided with a well-adhering and highly lustrous nickel coating which required no further polishing treatment.

Example VII Effects similar to those of Example VI were obtained by adding to the nickel-plating bath of that example 0.5-1 gm. N,N-pentamethylene-dithiocarbamic acid-n-propylesteem-sodium sulfonate and electroplating at room temperature and current densities between 4 and 8 amp./dm. 1

Example VIII The same highly lustrous nickel plate was obtained by substituting an equal amount of unsubstituted dithiocarbamic acid-n-propylester-w-sodium sulfonate for the sulfonate of Example VII, and electroplating at the same conditions of temperature and current densities as those stated in Example VII.

Example IX v 0.5 to 1 gm. of N,N-dimethyl-dithiocarbamic acid-npropylester-w-sodium sulfonate was dissolved in each liter of a zinc electroplating bath containing 200 gm. zinc sulfate and 1 gm. glacial acetic acid per liter of solution. Sheet steel electroplated in such a solution at room temperature and current densities between 4 and 9 amp./dm. was plated With a highly lustrous zince coating which did not need to be polished after rinsing. Without the addition of the above sulfonate, the zinc coating was dull and required polishing to give it luster.

Instead of the electroplating baths described above, other electroplating solutions for depositing chromium, tin, precious metals and the like may be used, and various other modifications and changes may be made from the above description without departing from the spirit of our invention or the scope of the following claims.

We claim:

1. An electroplating bath for producing deposits of metals selected from the group consisting of nickel, copper, zinc, silver, bronz and brass, comprising an acid solution of an inorganic salt of the metal to be deposited and a compound selected from the group consisting of organic sulfonic acids having the general structural formula and their salts, wherein G is an organic radical which includes a carbon atom bonded exclusively with three hetero atoms, one of which is a sulfur atom through which said organic radical G is linked to the radical R-SO H, the other two hetero atoms being selected from the group consisting of nitrogen, sulfur and oxygen atoms, and R is a bivalent aliphatic radical, said compound being added in a quantity sufficient to produce a bright metal deposit.

2. The process of producing bright and lustrous deposits of metals selected from the group consisting of nickel, copper, zinc, silver, bronze and brass which comprise electrodepositing said metal from a bath containing said metal principally in the form of an acid solution of an inorganic salt of the metal in the presence of a brightening agent selected from the group consisting of organic sulfonic acids having the general structural formula and their salts, wherein G represents a carbon atom group consisting of a carbon atom linked exclusively to three hetero atoms, one of which is a sulfur atom which links the carbon atom to the radical R, the other two hetero atoms being selected from the group consisting of nitrogen, sulfur and oxygen atoms, and R is a bivalent aliphatic radical, said compound being added in a quantity sufficient to produce a bright metal deposit.

3. An electroplating bath for producing deposits of and their salts, wherein X and Y each represent an atom selected from the group consisting of oxygen, nitrogen and sulfur, and R is a bivalent aliphatic radical.

4. The process of producing bright and lustrous electrodeposits of metals selected from the group consisting of nickel, copper, zinc, silver, bronze and brass which comprises electrodepositing said metal from a bath containing said metal in the form of an acid solution of an inorganic salt of the metal in the presence of about 0.01 to 20 gm. per liter of a brightening agent selected from the group consisting of organic sulfonic acids having the general structural formula selected from the group consisting of and their salts, wherein X and Y each represent an atunl selected from the group consisting of nitrogen, sulfur and oxygen, and R is a bivalent aliphatic radical.

5. An electroplating bath as in claim 1, said bivalent aliphatic radical being substituted.

6. An electroplating bath as in claim 1, said bivalent aliphatic radical being unsubstituted.

7. A process as in claim 2, said bivalent aliphatic radical being substituted.

8. A process as in claim 2, said bivalent aliphatic radical being unsubstituted.

9. An electroplating bath for producing deposits of metals selected from the group consisting of nickel, copper, zinc, silver, bronze and brass comprising an acid solution of an inorganic salt of the metal to be deposited and 0.01 to 20 gm. per liter of a compound selected from the group consisting of organic sulfonic acids having the general structural formula and their salts, wherein X and Y each represent an atom selected from the group consisting of nitrogen, oxygen and sulfur, and R is a bivalent aliphatic radical.

10. An electroplating bath as in claim 9, said bivalent aliphatic radical being substituted.

11. An electroplating bath as in claim 9, said bivalent aliphatic radical being unsubstituted.

12. The process of producing bright and lustrous deposits of metals selected from the group consisting of nickel, copper, zinc, silver, bronze and brass which comprises electrodepositing said metal from a bath containing said metal in the form of an acid solution of an inorganic salt of the metal in the presence of about 0.01 to 20 gm. per liter of a brightening agent selected from the group consisting of organic sulfonic acids having the general structural formula References Cited in the file of this patent UNITED STATES PATENTS 2,389,181 Brown Nov. 20, 1945 2,424,887 Henricks July 29, 1947 2,648,627 Donnelly Aug. 11, 1953 2,663,684 Pierce Dec. 22, 1953 

1. AN ELECTROPLATING BATH FOR PRODUCING DEPOSITS OF METALS SELECTED FROM THE GROUP CONSISTING OF NICKEL, COPPER, ZINC, SILVER, BRONZ AND BRASS, COMPRISING AN ACID SOLUTION OF AN INORGANIC SALT OF THE METAL TO BE DEPOSITED AND A COMPOUND SELECTED FROM THE GROUP CONSISTING OF ORGANIC SULFONIC ACIDS HAVING THE GENERAL STRUCTURAL FORMULA 